The application of high frequency electrical energy for coagulation is common in many surgical procedures. Coaxial bipolar coagulators are often used in surgical procedures such as ophthalmic procedures where discrete application of coagulation energy is required to stop bleeding. The term “bipolar” is used when describing a coagulator that has two separate conductive paths (also referred to as poles or electrodes) contained within the device, where one pole can act as the current source and the other as the electrical return or ground. In contrast, a monopolar device contains one conductive pole, such as the current supply, and the other pole or ground electrode is external to the device.
Disposable coaxial bipolar coagulators are handheld devices that have an electrical connector at the proximal end of the instrument and a slender coaxial bipolar probe tip at distal end. The electrical connector consists of two protruding pins for connection to a bipolar electrosurgical generator console which supplies the high frequency coagulating current. The coaxial bipolar tip is a slender probe consisting of two conductive poles electrically isolated from one another where the ends of both terminate in close proximity to one another at the distal end of the probe tip. The probe tip is constructed of two conductors in a coaxial relation where the one resides inside the other and the two are isolated by a concentrically disposed dielectric such as plastic. The outer conductor is often a stainless steel tube and the inner is often a stainless steel wire coated with a plastic dielectric. In use, contact of the distal tip poles with tissues and fluids enables the conduction of high frequency current between the tip poles and through the surrounding tissues and fluids for localized coagulation.
Poor coagulation performance, from insufficient power delivery as well as non-functioning units, typically from bad electrical connection or short circuit, are common deficiencies of existing coaxial bipolar coagulator devices and a frequent source of complaint from end users.
A common difficulty with bipolar coaxial coagulators has been to electrically connect the coaxial inner and outer conductors of the tip with the electrical connector at the proximal end of the device. Historically, these devices include an electrical assembly in which the inner and outer conductive electrodes of the coaxial bipolar tip are each coupled one to each of the electrical connector pins that form the two pin connector. Sometimes one or both the inner and outer coaxial tip electrodes are connected directly one to each of the connector pins, and sometimes one or both of the tip electrodes are connected indirectly one to each of the pins using an intermediate conductive element such as a wire. Whether one of the tip electrodes is fastened directly to one of the connector pins, requiring at least one connection or indirectly, requiring two or more connections, all of these connections are made by use of mechanical fastening methods such as welding, soldering, and/or crimp connection. An example of a crimp connection is when one or more conductive elements, such as a wire, are placed inside a channel, sleeve or other opening in a malleable conductive component. The opening is then squeezed closed securing the wire in the opening.
In fastening the conductive elements together, an electrical assembly is made in which the inner and outer conductors of the coaxial probe tip are mechanically attached to the connector pins. This electrical assembly is then retained within a plastic handle in either of two manners. One method is to place the assembly into a premolded handle consisting of two or more pieces which is then secured around the assembly by such methods as gluing, press-fit or ultrasonic welding.
Another method is to over-mold the electrical assembly to create the device handle. In the process of over-molding, the electrical assembly is placed into a mold tool where the portion of the assembly to be over-molded with the plastic handle resides inside the mold cavity, and the components which will protrude from the device handle, such as the tip and connector pins, project outside the cavity. The handle is then formed around the electrical assembly by injection of plastic (typically thermoplastic). Once the plastic is cooled and solidified, the unit is removed from the mold and the device assembly with an over-molded handle is complete.
A common problem with the assembly methods described above is that if one of the mechanically fastened components or if one of the connections breaks or fails due to stress or fatigue, the circuit can become open and the device will not function.
In the case of over-molding the device handle, the process of encapsulation and shrinkage of the polymer as it cools assists in secure retention of components contained within and protruding from the molded handle. However, a side effect from the over-molding technique is that the stresses from the over-molding process, including polymer injection and plastic shrinkage as it cools from elevated temperatures, can induce sufficient stress and tension on the components and connections that can ultimately lead to breakage and electrical failure of the device, if not immediately following molding, then sometime in the future. As a result, the over-molded components and connections forming the electrical assembly need to be sufficiently strong and secure to avoid subsequent electrical failure.
In the case of the electrical assembly being placed into a pre-molded handle, the high stresses from polymer injection and material shrinkage from cooling found during insert molding are not present as the handle is molded prior to assembly. However, the electrical assembly and protruding components are also not as inherently secure within the handle. Therefore, greater attention must be paid to securing components (particularly protruding functional components) to prevent or limit their movement as well as prevent unwanted stress on components and connections that could lead to device failure. An additional problem can arise once the components are secured within the pre-molded handle. The sterilization of surgical devices often requires exposure to an elevated temperature. If the electrical assembly is sufficiently retained within the pre-molded handle, thermal expansion of the polymer handle can result in damaging stresses to the electrical assembly components and connections similar to those which can occur during over molding.
A common drawback with the above-described methods of manufacture is the relatively costly and laborious additional process of mechanically fastening the electrical connections between the components that comprise the coaxial tip conductors, pin connectors and intermediate circuit elements, if applicable, that form the device's electrical circuit assembly prior to incorporation into the device handle, for without doing so, the conductive integrity between these components within the finished device is not assured.
Another problem with coaxial bipolar coagulators manufactured by the methods described above is that of axial migration or movement of one or more of the coaxial tip elements which can cause unwanted misalignment of the distal tip geometry. Thermal expansion and contraction of the device handle can place stresses on the components and connections within the device as described above. In addition to causing mechanical failure of these components and connections, these stresses can also cause the inner and outer conductive elements of the coaxial tip to shift axially against one another causing an unwanted misalignment of the distal tip profile, such as a retraction of the inner conductive pole which can reduce tissue contact and diminish coagulation performance.
Coagulation performance is important to surgeons. This is particularly the case for eye surgeons as there is often need to quickly stop unwanted bleeding before it obscures visibility, as well as to coagulate thoroughly so as to prevent unwanted post operative bleeding. New ophthalmic surgical techniques utilizing smaller incisions have created the need for bipolar coaxial coagulators with increasingly smaller tip diameters. As the coaxial tip becomes smaller in diameter, the ability of the device to deliver coagulation power is diminished, and it is therefore increasingly difficult to provide sufficient coagulation power to thoroughly address unwanted bleeding. A further complication of the variation in power delivery between different tip designs occurs frequently when two bipolar coagulators of sufficiently differing tip diameter are used in back-to-back cases or as often happens are used in the same case. Because these units often require significantly different power settings to achieve the desired coagulation results, it is not just an inconvenience but also a matter of safety that the power setting on the console be adjusted to the correct setting. This is particularly important when the power needs to be adjusted from high to low prior to use to avoid unwanted injury.
What makes a non-functioning, or seemingly non-functioning, bipolar coagulator such a big problem for the surgeon is that it is frequently only discovered when he or she attempts to coagulate tissue with the device during a surgical procedure. Most commercially available bipolar electrosurgical generators have a visible light and/or audible tone on the console to indicate when the power is activated and being supplied to the console output terminals. However, if a handpiece or power cord is improperly connected or if there is a fault in either the handpiece or cord, there is no ready means to verify that power is being applied to the hand unit before attempting to use the device. Therefore, if a bipolar coagulator unit appears to not be working properly, a common occurrence is to then troubleshoot the cause during the surgical procedure in a manner similar to the following: First is to typically check the settings on the generator and verify all electrical connections. If no fault is found there they might then try to turn up the power setting on the generator and the surgeon would try it again. If that does not correct or overcome the problem, then next would be to replace either the power cord and/or the bipolar coagulator handpiece with a new unit in an effort to remedy the fault, and again the surgeon would re-try the coagulator to see if it is functioning. The delay in treatment caused by this type of fault, as well as the procedure to remedy it is something that many eye surgeons know well, and it is more than just an aggravation. It can also become an issue of safety as not only is treatment delayed, but other complications such as impaired visibility may arise.